This master’s thesis deals with the plasmon resonance of the nanostructures of several selected tungsten oxides using Fourier transform infrared spectroscopy (FTIR spectroscopy). The physical principles of the plasmonics, the characteristics of the materials used, as well as the principle of operating and measuring on the FTIR spectrometer, are described in the first part of this thesis. The second part is focused on the preparation of samples and performing measurements on the FTIR spectrometer. This part ends by representing the final spectra and the results obtained.

Les plasmons de surface (SP) sont des ondes électromagnétiques se propageant à l'interface entre deux milieux, typiquement un métal et un diélectrique. Les plasmons de surface ont la capacité de confiner le champ électromagnétique dans de très petite région de l’espace, typiquement quelques nanomètres, c’est à dire bien en dessous de la limite de diffraction de la lumière. Une conséquence de ce confinement sub-longueur d’onde de la lumière est que leur observation nécessite une résolution spatiale nanométrique - ce qui exclut l’utilisation de techniques optiques standard. Néanmoins, le microscope électronique en transmission à balayage (STEM) est un outil particulièrement adapté à l'étude des plasmons de surface car il emploie des électrons rapides ayant une longueur d’onde typique comprise entre 1 et 10 picomètres. Ainsi, durant la dernière décennie, les spectroscopies électroniques appliquées à la nano-optique se sont fortement développées, parmi elle comptent : la spectroscopie de perte d'énergie électronique (EELS), la spectroscopie cathodoluminescence (CL) ou l'interférométrie de Hanbury Brown et Twiss (HBT) appliquée à la CL. Dans cette thèse, j’ai exploré différents problèmes ouverts de la plasmonique et de la nano-optique dans le cadre particulier de la microscopie électronique. Dans le chapitre 3, je présente un formalisme prenant en compte à la fois la nature quantique et relativiste des expériences d’EELS en faisant appel notamment à des éléments de théorie quantique des champs. Dans le chapitre 4, nous démontrons que la réalisation d’une expérience d’EELS avec de tels faisceaux permet de mesurer des propriétés jusqu’alors inatteignable à l’échelle du nanomètre telle que la phase des plasmons, leurs chiralité optique voire même leur longueur de cohérence. Dans le chapitre 5, je présente plusieurs résultats théoriques et expérimentaux concernant des expériences de couplage. En particulier, j’étudie le phénomène contre-intuitif d’auto-hybridation qui est une conséquence de la nature non-hermitienne du problème aux valeurs propres associé aux résonances de plasmon et établit une analogie avec les systèmes quantiques ouverts. Enfin, au chapitre 6, je discute des récentes mesures de phonon réalisées dans un STEM grâce au développement de monochromateur électroniques. / Surface plasmons (SP) are electromagnetic waves propagating at the interface between two media typically a metal and a dielectric. SPs can confine electromagnetic fields in very short volumes (typically one to few nanometers), well below the light diffraction limit. This property has a tremendous number of applications ranging from fundamental physics (e.g. quantum optics) to applications (e.g. cancer therapy). However, the price to pay is that SPs suffer from huge ohmic losses in the metal which leads to very short lifetimes (typically few femtoseconds). Theoretically, this presence of dissipation dramatically hardens the theoretical description of SPs. Another consequence of the sub-wavelength confinement of light associated with SPs is that their observation requires a nanometric resolution - which excludes the use of standard optical techniques. Yet, the scanning transmission electron microscope (STEM) is a particularly suitable tool to study SPs as it employs fast electrons with typical wavelength from 1 to 10 picometers. Thus, the last decade has seen the tremendous development of electron-based spectroscopies applied to nano-optics such as electron energy loss spectroscopy (EELS), cathodoluminescence spectroscopy (CL) or STEM- Hanbury Brown and Twiss interferometry (HBT). In this thesis, I explored different open problems of plasmonics and nano-optics under the scope of electron microscopy and spectroscopies. In chapter 3, I develop a formalism taking into account both the quantum and relativistic nature of EELS experiments using elements of quantum field theory. In chapter 4, I apply the latter formalism to the case of EELS measurements of SPs using electrons with shaped phase. In chapter 5, I give several theoretical and experimental results on coupling experiments involving SPs. Particularly, I demonstrate a counterintuitive type of coupling, the so-called self- hybridization which is a consequence of the non-Hermitian nature of the LSP eigenproblem and draw analogy with open quantum system. Finally, in chapter 6, I discuss the recent result on vibrational EELS in monochromated STEM.

Our work addresses a novel biocompatible plasmon-enhanced nanostructure approach based on the combination of metal nanoparticles, light emitting polymer-based nanostructures, and scalable cellulose nanofiber templates via a one-step facile electrospinning process that can easily be applied to biomedical devices. In collaboration with the Team of Prof. Lee Goldstein in the Boston University medical campus, we demonstrated light emission from small-size (below 200nm) polymer nanoparticles coupled to plasmonic nanoparticles and to light-emitting biocompatible molecules. In order to fully demonstrate the potential of our novel plasmonic nanostructures we developed Magnetic resonance imaging (MRI) reagent doped Polycaprolactone (Core)-Polyethylene glycol (shell) core-shell nanoparticles and studied their size distribution and dispersion properties in a phosphate buffered saline solution. Our materials were optimized in order to obtain no aggregation of the nanoparticles in solution. The presence of MRI reagent in nanoparticles were demonstrated via Inversion Recovery Sequences (IR) by characterizing the different T1 relaxation times. The concentration of Gd in the nanoparticles dispersion was estimated with different dilution of Gd commercial reagent as a reference. In addition, we combined facile electrospinning fabrication with top down nano-deposition and demonstrated a novel and scalable plasmonic resonant medium for rapid and reliable Raman scattering sensing of molecular monolayers and bacteria. Specifically, aided by PCA multivariate data analysis techniques, we demonstrated fingerprinting Surface Enhanced Raman Scattering (SERS) spectra of different bacteria strains (E. Coli K12, E. coli BL21 (DE3) and E. coli DH 5α) entrapped in our novel plasmonic networks. Finally, in this thesis we have also addressed the development of novel, Si-compatible and largely tunable plasmonic materials for biosensing applications in the mid-infrared spectral range and developed a novel type of transparent conductive oxide based on the Indium Silicon Oxide (ISO) material (Indium Silicon Oxide) that features enhanced surface smoothness and thermal stability compared to Indium tin oxide (ITO) and Titanium nitride (TiN) alternative plasmonic materials. In collaboration with our collaborators at Columbia University, we demonstrated the tunability of near-field plasmonic resonances from 1.8 to 5.0 μm as a function of different annealing temperature. This work provides an enabling first-step towards the development of novel Si-compatible materials with tunable plasmon resonances for metamaterials and sensing devices that operate across the infrared spectrum. / 2019-07-02T00:00:00Z

<p>In the realm of tunable optical devices, 3D nanostructures with metals and dielectrics have been utilized in a wide variety of practical applications ranging from optical switching to beam-steering devices. 2D materials, on the other hand, have enabled the exploration of truly new physics unattainable with 3D systems due to quantum confinement leading to unique optical properties and enhanced light-matter interactions. Transdimensional materials (TDMs) – atomically thin films of metals – can couple the robustness of 3D nanostructures with the new physics enabled by 2D features. However, the evolution of the optical properties in the transdimensional regime between 3D and 2D is still underexplored. The optical properties of metallic TDMs are expected to show unprecedented tailorability, including strong dependences on the film thickness, composition, strain, and surface termination. They also have an increased sensitivity to external optical and electrical perturbations, owing to their extraordinary light-confinement. Additionally, the small atomic thicknesses may lead to strongly confined surface plasmons and quantum and nonlocal phenomena. The strong tunability and light-confinement offered by TDMs have resulted in a search for atomically thin plasmonic material platforms that facilitate active metasurfaces with novel functionalities in the visible and near infrared (NIR) range. In this research, we explore the plasmonic properties and tailorability of atomically thin titanium nitride (TiN). We experimentally and theoretically study the thickness-dependent optical properties of epitaxial TiN films with thicknesses down to 1 nm to demonstrate confinement induced optical properties. Overall, this research demonstrates the potential of TDMs for unlocking novel optical phenomena at visible and NIR wavelengths and realizing a new generation of atomically thin tunable nanophotonic devices. </p>

Designing photonic-plasmonic nanostructures with desirable electromagnetic properties is a central problem in modern photonics engineering. As limited by available materials, engineering geometry of optical materials at both element and array levels becomes the key to solve this problem. In this thesis, I present my work on the development of novel methods and design strategies for photonic-plasmonic structures and metamaterials, including novel Green’s matrix-based spectral methods for predicting the optical properties of large-scale nanostructures of arbitrary geometry. From engineering elements to arrays, I begin my thesis addressing toroidal electrodynamics as an emerging approach to enhance light absorption in designed nanodisks by geometrically creating anapole configurations using high-index dielectric materials. This work demonstrates enhanced absorption rates driven by multipolar decomposition of current distributions involving toroidal multipole moments for the first time. I also present my work on designing helical nano-antennas using the rigorous Surface Integral Equations method. The helical nano-antennas feature unprecedented beam-forming and polarization tunability controlled by their geometrical parameters, and can be understood from the array perspective. In these projects, optimization of optical performances are translated into systematic study of identifiable geometric parameters. However, while array-geometry engineering presents multiple advantages, including physical intuition, versatility in design, and ease of fabrication, there is currently no rigorous and efficient solution for designing complex resonances in large-scale systems from an available set of geometrical parameters. In order to achieve this important goal, I developed an efficient numerical code based on the Green’s matrix method for modeling scattering by arbitrary arrays of coupled electric and magnetic dipoles, and show its relevance to the design of light localization and scattering resonances in deterministic aperiodic geometries. I will show how universal properties driven by the aperiodic geometries of the scattering arrays can be obtained by studying the spectral statistics of the corresponding Green’s matrices and how this approach leads to novel metamaterials for the visible and near-infrared spectral ranges. Within the thesis, I also present my collaborative works as examples of direct and inverse designs of nanostructures for photonics applications, including plasmonic sensing, optical antennas, and radiation shaping.

Upconverted light from nanostructured metal surfaces can be produced by harmonic generation and multi-photon luminescence; however, these are weak processes and require extremely high field intensities to produce a measurable signal. Here we report on bright emission, five orders of magnitude greater than harmonic generation, that can be seen from metal tunnel junctions due to light-induced inelastic tunneling. Like inelastic tunneling light emission, which was recently reported to have 2% conversion efficiency per tunneling event, the emission wavelength recorded varies with the local electric field applied; however, here the field is from a 1560 nm femtosecond pulsed laser source. Finite-difference time-domain simulations of the experimental conditions show the local field is sufficient to generate tunneling-based inelastic light emission in the visible regime. This phenomenon is promising for producing ultrafast upconverted light emission with higher efficiency than conventional nonlinear processes. / Graduate

Au cours de ma thèse, j'ai développé un procédé de fabrication spécifique capable de produire un biocapteur qui combine deux techniques de biodétection différentes, la réponse plasmonique basée sur la résonance de plasmon de surface localisée (LSPR) et la réponse électrochimique. Les méthodes et les résultats qui sont présentés dans ce manuscrit ont été définis pour converger vers un dispositif fluidique unique combinant ces deux approches de détection différentes. Afin de trouver la configuration permettant l'excitation des résonances plasmoniques, la géométrie des nanocavités MIM (métal/isolant/métal) en réseau de lignes interdigitées a été optimisée par des simulations électromagnétiques. La fabrication par nanoimpression douce assistée UV (SoftUV-NIL) a été optimisée et, finalement, la caractérisation optique de ces nanocavités a été comparée avec succès aux simulations théoriques. Parallèlement à la réalisation de ce dispositif nanostructuré, des dispositifs électrochimiques fluidiques plus simples qui intègrent des microélectrodes classiques ont également été développés. L'objectif était d'abord de développer une chimie innovante pour le couple « biotine/streptavidine » et de comprendre ensuite comment les paramètres fluidiques peuvent affecter l'efficacité de capture des biomolécules. Ce manuscrit se termine par une discussion sur le rôle des paramètres fluidiques concernant l’efficacité de la biodétection sur la base de la théorie de Squires. / During my thesis, I worked on the development of a specific fabrication process able to produce a device that combines two different biodetection techniques, plasmonic response based on Localized Surface Plasmon Resonance (LSPR) and electrochemical response. Methods and results that are presented in this manuscript were defined to converge towards a unique fluidic device combining these two different sensing approaches. This device integrates interdigitated array of MIM nanocavities. In order to find the easier working configuration allowing the excitation of plasmonic resonances, their geometry has been optimized through electromagnetic simulations. The fabrication of these dual devices has been optimized based on Soft-UV NIL and, finally, optical characterization of these nanocavities has been successfully compared with theoretical simulations. In parallel to this challenging goal, simpler fluidic electrochemical devices that integrate conventional microelectrodes have also been developed. The goal was first to develop an innovative chemistry for the couple biotin/streptavidin and secondly to learn how fluidic parameters can affect the capture efficiency of molecules. This manuscript ends with a discussion on the role of the fluidic parameters on the biodetection efficiency based on the theory of Squires.

The rational combination of dielectric and metallic nano particles brings novel optical properties to conventional subwavelength structures. This thesis introduces the optoplasmonic geometries demonstrating versatile ability in both far and near field modification within nano scale. Template-assisted self-assembly approaches are applied creating nano entities with titanium dioxide and gold nano spheres. A top-bottom mono hybrid unit and interdigitated array are developed. With the examination of the elastic and inelastic response of these hybrid materials, physical models are simulated to depict the scenario of varied geometry and combination of nano particles. In contrast to solely metal or dielectric particle arrays, this type of artificial material not only enhances the near electric field intensity within the metal nano cluster hot spots, but also expands the overall volume of enhanced electric field. Further study reveals that the additional enhancement and redistribution of near field are derived from the coupling between the nano gold cluster plasmon resonance and the in-plane diffractive mode of the dielectric array. The redirected emission profile of the fluorescent dyes within the hybrid array is explored.

Les sources infrarouges basées sur des effets d'optique du second ordre constituent de très bons outils de spectrométrie des polluants présents dans l'atmosphère, grâce notamment à leur grande accordabilité spectrale. Ils demandent toutefois une forte puissance lumineuse incidente et une grande quantité de matériau non linéaire pour être efficaces. On peut les rendre très compactes en réalisant la conversion de fréquence à l'aide de nanostructures plasmoniques contenant des inclusions diélectriques présentant une susceptibilité du deuxième ordre non nulle. La lumière y est très fortement concentrée à la résonance augmentant fortement la quantité de polarisation non linéaire produite, afin d'y exalter les effets d'optique non linéaire.Ce travail s'attaque d'abord à la conception de nano-résonateurs grâce au développement d'un outil de simulation d’empilements nanostructurés selon une dimension. Trois architectures sont étudiées : les nanorésonateurs de type sillon, les nanorésonateurs de Helmholtz et les guides d'ondes à résonances de modes guidés. Dans chaque cas, le dimensionnement passe par la détermination de géométries bi- voire tri-résonantes pour la réalisation d'accord de modes en génération de second harmonique ou de différence de fréquences.La fabrication en salle blanche des résonateurs sillons et guides d'ondes est ensuite exposée, suite à un important travail de développement technologique, qui a permis l’obtention d’échantillons de très bonne qualité. / Infrared sources based on second order effects are interesting tools for atmospheric pollutants spectrometry thanks to their wide tunability. Such effects nevertheless demand strong incident powers or massive non linear crystals to be efficient. A new way to reduce their size consists in realizing frequency conversion with the help of plasmonic nanostructures containing dielectric inclusions showing a non zero second order susceptibility. Light is greatly harvested and concentrated at resonance leading to the creation of a great quantity of non linear polarization, so as to further enhance non linear optics effects.This work begins with a study of nanoresonators through developing a simulation tool for one dimensional nanostructured multilayered structures. Three architectures are retained : slit nanoresonators, optical Helmholtz nanoresonators and waveguides based on guided mode resonances. In every case, the conception focuses on the finding of bi- and even of tri-resonant geometries to achieve mode matching for second harmonic of difference frequency generation.Clean room fabrication is then detailed step by step following the important works that have permitted the fabrication of samples showing a very good quality.

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